1. Field of the Invention
This present invention relates in general to secondary cells and, more particularly, to an electrolytic cell and electrolytic process associated therewith, wherein the interfacial resistance of the working electrode is substantially lowered and sustained over the life of the electrolytic cell.
2. Background Art
Rechargeable, or secondary electrolytic cells, have been known in the art for many, many years. Furthermore, secondary cells constructed with lithium anodes have likewise been known in the art. Although such rechargeable lithium batteries have proven to be functional, many of such batteries have been undesirable from a practicle standpoint due to one, or both, of the following shortcomings: 1) the cycle life of such lithium batteries are relatively short (compared to other types of secondary cells, such as nickel-cadmium) due to the formation of dendritic growth on the lithium electrode during electrodeposition; and/or 2) the inability to effectively lower and substantially sustain the interfacial resistance at the lithium anode during the life of the rechargeable lithium battery.
With respect to suppression of dendritic growth, various approaches have been disclosed, including, but not limited to 1) the use of a copolymer layer applied to the surface of the lithium anode--wherein the copolymer layer is ionically conductive, electronically conductive when in contact with the lithium anode and which enables chemical equilibrium between the copolymer layer itself and the lithium anode (details relevant to such a layer can be found in U.S. Pat. No. 5,434,021); as well as 2) applying a continuous coating of an electronically conductive layer, such as graphite, to the surface of the lithium anode.
While such continuous electronically conductive layers have contributed to the suppression of dendritic growth--through their ability to provoke the formation of a substantially stable passivating layer at the anode--such continuous layers have also been responsible for lowering the cell's voltage, and, in turn, have shown little, if any, effect on lowering and sustaining interfacial resistance at the anode (when compared to anodes without such a layer). Indeed, when such a "continuous" layer is applied, the ions (associated with the anode, such as lithium ions which have passed into the electrolyte) chemically interact with the layer during, for example, reduction, wherein such an interaction chemically alters the composition of the electrode. For example, if the electrode is a lithium anode, and the layer is composed of carbon, the electrode will be altered during electrodeposition to an electrode composed of carbon and lithium (LiC.sub.6)--thereby lowering the cells voltage relative to the voltage when the lithium electrode is substantially unaltered during electrodeposition. As another example, if the electrode is a lithium anode and the layer is composed of aluminum, the electrode will be altered during electrodeposition to an electrode composed of lithium/aluminum alloy (LiAl), thereby lowering the cells voltage relative to the voltage when the lithium electrode is substantially unaltered during electrodeposition.
Furthermore, when such a continuous electronically conductive particulate is applied to an anode, the layer is typically comprised of a highly crystalline material, such as graphite, as opposed to a non-crystalline material, such as carbon black. Indeed, such a highly crystalline graphite layer has proven necessary, when applied in a continuous orientation on the surface of the anode, for purposes of enabling the particular ions from the electrode to pass through the continuous carbon layer during oxidation and reduction.